This project concentrates on two aspects of the structure of bacterial ribosomes. The first is details of the structure of ribosomal RNA and other ribosome-bound RNAs including tRNA and mRNA. Covalent crosslinking monitored by electron microscopy is used to map double stranded regions, single stranded regions, and more complex folding. Tritium exchange and fluorescence measurements are used to observe the structure of the smaller RNAs on the ribosome. Of special interest is RNA components of functional sites and topological aspects of RNA structure. The second focus is interactions between RNAs on the ribosome. Current interest include whether there are any functionally significant interactions between the rRNAs or between rRNA and tRNA. Additional studies are in progress on quantitative measurements of mRNA-ribosome interactions.